Electrical plasma-torch apparatus and method for applying coatings onto substrates



April 11, 1967 R. UNGER ETAL ELECTRICAL PLASMA-TORCH APPARATUS ANDMETHOD FOR APPLYING COATINGS ONTO SUBSTRATES Original Filed April 14,1965 3 Sheets-Sheet 1 FIG.3A

I N VIEN'I'ORS.

(/NGEIQ 2055B 7' 205527 F: BYE/4M April 11, 1967 R. UNGER ETAL 3,313,908

ELECTRICAL PLASMA-TORCH APPARATUS AND METHOD FOR APPLYING COATINGS ONTOSUBSTRATES Original Filed April 14, 1965 3 Sheets-Sheet 2 FIG.3 Q 755%"CUEIQEN T INVENTORS. SOMQCE 2055/2 7 (W952 205.52 r E B e/2M A7TO/Q/VEYS' A April 11, 1967 R. UNGER ETAL 13,908

ELECTRICAL PLASMA-TORCH APPARATUS METHOD FOR A LYING v COATINGS ONTOSUBS TES Original Filed April 14, 1965 3 Sheets-Sheet 5 INVENTORS.205527 (/NGEE ROBE/Q T E B Y/Qfl/W Y Q- Unite States atent 3,313,998Patented Apr. 11, 1967 Free ELECTRICAL PLASMA-TORCH APPARATUS AND METHODFOR APPLYING COATINGS ONTO SUBSTRATES Robert Unger, Dana Point, andRobert F. Byram, Santa Ana, Califi, assignors to Giannini ScientificCorporation, Amityville, N.Y., a corporation of Delaware Continuation ofabandoned application Ser. No. 448,065, Apr. 14, 1965. This applicationAug. 18, 1966, Ser. No. 573,431

18 Claims. (Cl. 219-76) The present patent application is a continuationof copending application Serial No. 448,065, filed April 14, 1965, forElectrical Plasma-Torch Apparatus and Method for Applying Coatings OntoSubstrates, now abandoned.

This invention relates to a plasma-torch apparatus and method forcreating extremely high particle velocities and thereby depositingsuperior-quality metal and/ or ceramic coatings on substrates of varioustypes. The invention further relates to a plasma torch incorporatingimproved arc [gas-introduction means, improved electrodes of the inserttype, and improved cooling means.

A primary object of the present invention is to provide an apparatus andmethod for effectively and efiiciently adhering coatings ontosubstrates, such coatings being characterized by a high degree ofdensity, smoothness and other desirable characteristics.

A further object is to provide a method of eifecting high-velocityspraying of particles of metals and ceramics onto substrates, in amanner achieving'numerous important results including effectivecollimation of the jet, minimum loss and wastage of powder, highdeposition rates and efficiencies, absence of undesired chemicaleffects, smooth coating surfaces, high coating density, and superioradherence to the substrate.

An additional object is to provide a plasma-torch apparatus and methodwhich may be readily adapted for optimum operation relative to eitherceramic spray or metal spray.

Another object is to provide a plasma-torch apparatus and method whereinthe arc gas is introduced in different ways in accordance with whethersuch gas is monatomic or diatomic, both ways producing a swirl or vortexaction, and both achieving benefits including increased electrode life.

A further object is to provide an electrical plasma-jet torch havingfront and rear electrodes formed as inserts which are inexpensive tomanufacture and use, and which may be replaced in a very short period oftime.

Another object is to provide a plasma torch incorporating an improvedwater-circulating system effecting a better degree of cooling of theelectrodes and other-torch components.

Another object is to provide a high-velocity powder spray apparatus andmethod wherein a cover-gas shield is employed in conjunction with thenozzle element to effect improved collimation of the jet, in addition toachieving benefits such as prevention of undesired (or creation ofdesired) chemical eifects, cooling of the workpiece, and removal of anyloosely-adherent spray particles.

These and other objects will become apparent from the following detaileddescription taken in connection with the accompanying drawings in which:

FIGURE 1 is a side elevational view illustrating the plasma torch of theinvention as employed in spray-depositing a coating onto a substrate,and showing various gas and powder sources in schematic form;

FIGURE 2 is an enlarged elevational view showing the front end of thetorch, looking upwardly in the showing of FIGURE 1;

FIGURE 3 is a longitudinal central sectional view taken on line 33 ofFIGURE 2;

FIGURE 3A is a longitudinal form of nozzle insert;

FIGURE 4 is a transverse sectional view on line 4-4 of FIGURE 3;

FIGURE 5 is a transverse sectional view on line 55 of FIGURE 3;

FIGURE 6 is a sectional view, on line 66 of FIG- URE 3, illustrating thearc gas inlet means which is employed for monatomic gases;

FIGURE 7 is a sectional View, on line 77 of FIG- URE 3, showing the arcgas inlet means which is employed for diatomic gasses; and

FIGURE 8 is a sectional view schematically indicating a powder feedmechanism employed in the present method and apparatus.

Proceeding first to a description of the entire apparatus the electricalplasma torch is illustrated to comprise an insulating handle and easing1d the lower portion of which is adapted to be gripped by the operator,and the upper portion of which is adapted to contain various housing andelectrode elements next to be described. One such element containedwithin the upper portion of insultating handle 10 comprises a cup-shapedinsulating body l l, formed of a phenolic or other suitable substance,such body being suitably grooved at the peripheral portions thereof toreceive the rims of generally cup-shaped rear and front housing elements12 and 13, respectively. Such housing elements, and the remainingportions of the torch (excepting for the seals, and unless otherwisenoted), are formed of copper, brass, tungsten, or other suitable metals.

The rear housing element 12 has a central tulbular stem 14 which extendsthrough a corresponding axial opening in the insulating body 11.Inserted into such stem in close-fitting relationship is the cylindricalbody of a rear electrode element 16. Such cylindrical body mergesthrough a forwardly-convergent frustoconical portion, and a second andsmaller-diameter cylindrical portion, with a generally conical arcingtip section 17 having a rounded forward or apex end. Such arcing tip 17is disposed in the nozzle passage to be described, whereas the rearelectrode sections between the arcing tip and the stem 14 are disposedin a gas-vortex chamber. The vortex chamber is defined by a cup-shapedliner 19 which nests closely in the cup-shaped insulating body 11. Theliner is suitable maintained in position as by screws 20'.

Rear electrode element 16 is maintained in position by means of anexternally-threaded plug 21 which is seated against the enlarged head orrear end 22 of such element. Plug 21 and head 22 are disposed in aninternally-threaded section of hollow stem 14, but only the plug isshown as being threadedly associated with the stem.

The portion of insulating handle and casing 10 axially adjacent plug 21is provided with an opening 23, so that the plug 21 may be unthreaded(as by inserting a wrench into a hexagonal socket therein) in order toremove the entire rear electrode 16. In the described manner, therefore,the rear electrode may be replaced easily and in a very short period oftime. A cover plug, not shown, may be removably mounted in opening 23.

The above-indicated liner 19 for the gas-vortex chamber 18 may be formedof a suitable insulating material such as asbestos cement. The internalwall of such liner is cylindrical and concentric with the axis of thetorch apparatus. Provided in the insulating body 11 between the bottom(rear) wall of liner 19 and the bottom wall of the body 11, and aroundstem 14, is an annulus or counterbore 24.

Defined between the bottom wall of rear housing 12 and the adjacent(radial) wall of body 11 is a coolant sectional view of one 3 chamber 26through which water or other coolant for the rear electrode is passed aswill be described subsequently. The front housing element 13 alsodefines therein, on opposite sides of a water separator to be described,several coolant chambers adapted to cool the nozzle element and adjacentportions of the torch.

The front and rear housings 13 and 12 face in opposite directions, therims thereof being seated over annularlygrooved portions of body 11 aspreviously indicated. Such rims are suitably secured to the body 11, asby screws 27 some of which are indicated in FIGURE 5. Such screws, andcooperating O-rings 28 and 29, effectively maintain the parts inassembled relationship and prevent leakage of water or other coolantfrom the housmgs.

A powder-injection, cooling and electrode-supporting member 31 ismounted to front housing 13 as by screws 32 (FIGURE 2) which extendthrough a radial flange 33 of such member. On the forward side of flange33, and preferably integral therewith, is a relatively large-diametercylindrical portion 34 of the element 31. Integrally formed on the otherside of flange 33 is a relatively smalldiameter cylindrical portion 36having axially-spaced radial flanges 37 and 38 at the inner end thereof.

The forwardmost of the two flanges 37 and 38 on smalldiametercylindrical portion 36 is numbered 37. Such flange seats a generallyfrustoconical hollow water separator or partition 39 which extendsoutwardly therefrom and seats against the forward face of insulatingbody 11 adjacent the interior surface of housing 13. Thus, forward andrear coolant chambers 41 and 42 are defined on opposite sides ofseparator 39, within housing 13 and radially-outwardly of thecylindrical portion 36.

The inner or rearward one 38 of the indicated flanges on portion 36seats against the forward edge of the liner (or wall member) 19 for thearc chamber 18. Furthermore, such flange 38 engages the interior surfaceof the cup-shaped body 11. An O-ring 43 provided at such interiorsurface, and a second O-ring 44 provided around stem 14 and engaging thebody 11, insure against leakage of gas from the arc chamber 18.

Provided continuously through both the forward and rear portions 34 and36 of the powder-injection, cooling and electrode-supporting member 31is a cylindrical passage or bore 46. A nozzle and front electrode insert47, having a cylindrical surface, is mounted in such bore 46. The nozzleinsert is mounted in close-fitting but removable relationship, beingsecured by means of the set screw 48 indicated in FIGURE 4. Such setscrew 48 is threaded radially through the relatively large-diametercylindrical section 34 of element 31, and has a conical inner end whichseats in a conical recess in the periphery of the nozzle insert 47. Thepositions of the set screw and recess are such that insert 47 will bemaintained in a predetermined desired position within element 31, theposition being such that powder-injection passage (to be describedhereinafter) will register precisely.

The nozzle and electrode insert member 47 has formed therethrough aplasma and powder passage having a cylindrical forward portion (or bore)49 and a-frustoconical rear portion 51. Both of such portions arecoaxial with chamber 18 and with rear electrode 16. The cylindricalforward portion 49 is relatively long, for purposes to be described. Therear portion 51 is sufficiently large in diameter to receive the conicalforward or arcing section 17 of the rear electrode. Such electrodesection 17 is much smaller in diameter than is the adjacent region ofpassage portion 51, so that are gas may flow forwardly and tangentially(helically) from vortex chamber 18 into passage portion 49.

There will next be described the remaining portions of the passages andchambers through which water (or other coolant) is circulated in orderto cool effectively the described nozzle insert 47 and also the rearelectrode 16..

Water from a suitable source is conducted inwardly through an inlet pipeor conduit 52. which extends through insulating handle 10 andcommunicates with the abovedescribed chamber 41 on the forward side ofwater separator 39. From chamber 41, the water circulates forwardly intoand through two circumferentially-spaced water passage 53 (FIGURES 3 and4) in member 31. Such passages 53 communicate with an annular chamber 54which is formed at the forward end of the large-diameter portion 34 ofmember 31. Chamber 54, in turn,

communicates with a large number of circumferentiallyspaced waterpassages 56 (FIGURES 3 and 4), such passages having relatively smalldiameters and extending longitudinally of the torch and closely adjacentthe outer cylindrical wall of nozzle insert 47. Thus, such insert 47 iseffectively cooled by the water which flows (in opposite directions)over and through the member 31.

Passages 56 communicate with the above-described chamber 42 on the rearside of separator 39. From such chamber 42, the water flows rearwardlythrough a substantial number of circumferentially-spaced longitudinalpassages 57 (FIGURES 3 and 5) in the insulating body 11. The water isthus conducted to the described chamber 26 at the rear of the torch, anddischarges through a water-outlet pipe or conduit 58 in handle 10.

Leakage of water from the coolant circuit is prevented by thepreviously-indicated O-rings and also by an additional O-ring 59 whichis provided bet-ween the radial front face of housing 13 and theadjacent flange 33 of member 31.

Electrical power may be supplied to the torch in any suitable way, butis preferably delivered through the 7 Water inlet and outlet conduits 52and 58, in order that the power conduits will be water cooled and thusprevented from overheating. For this purpose, the conduits may be formedof metal but, preferably, are formed of flexible insulating material andcontain flexible electrical conductors (not shown) in the waterpassages. As shown in FIGURE 3, a suitable current source 61 isconnected through a lead 62 to water-outlet conduit 58, and through asecond lead 63 to the water-inlet conduit 52.

Current source 61 is preferably a DO. source adapted to deliver veryhigh currents, the lead 63 being connected to the positive terminal andlead 62 to the negative. Thus, the nozzle insert and electrode 47 isnormally the anode, whereas the rear electrode 16 is normally thecathode. It is to be understood, however, that reverse polarities may insome cases be employed, as may alternating current, pulsating current,high-frequency current, combination DC. and superimposed high-frequencycurrent, etc.

The current source 61 operates, after use of a suitable high-frequency,high-voltage or other arc-starting means (not shown), to maintain ahigh-current electric are 65 (FIGURE 3) between the tip or forward endof rear electrode portion 17 and the wall of cylindrical nozzle insertportion 49. Preferably, the gas-flow and other conditions are caused tobe such that the are (at the downstream footpoint thereof) engages thewall of passage portion 49 at a region which is spaced a verysubstantial distance rearwardly from the downstream (forward) end ofinsert 47. Such downstream arc footpoint is located upstream of thepowder-injection port to be described. It is to be understood that theare 65 is indicated only in schematic fashion.

Proceeding next to a description of the means for introducing arc gasinto vortex chamber 18, this includes first and second ports or inletopenings 66 and 67 which are formed in the chamber liner 19 as shown inFIG- URES 3, 6 and 7. The first port 66 is located in the bottom (rear)corner of the liner 19 and communicates radially, through a passageportion 68 (FIGURE 7) in insulating body 11, with an internally-threadedfitting receptacle or socket portion 69 also formed in such body.

The second port, number 67 is disposed forwardly of port 66 andcommunicates through an oblique passage portion 71 with the indicatedfitting receptacle 69. Such oblique portion 71 is directedradially-inwardly and forwardly, and is preferably at an angle ofbetween about 60 degrees and about 70 degrees relative to thelongitudinal axis of the plasma torch apparatus.

Both of the ports 66 and 67 are olfset substantial distances from avertical plane intersecting the longitudinal axis of the torch, so thatthe gas introduction is generally tangential relative to the gas-vortexchamber 18. Referring to FIGURE 6, when the gas is flowing throughpassage 71 and port 67 the gas flows not only tangentially but alsoforwardly and helically, the pitch or lead of the helix being relativelygreat. On the other hand, when gas is flowing through passage 68 andport 66 there is a substantially purely tangential manner of gasintroduction, with much less forward inclination and with a resultinghelical gas fi'ow characterized by less lead or pitch in the helix.

First and second externally-threaded fittings 73 and 74 are adapted tobe selectively inserted into the internally-threaded fitting receptacleor socket 69, to thereby cause inflow of gas either through passage 68and port 66, or through passage 71 and port 67. The first such fittingis shown in FIGURE 7 and has an axial bore 76 communicating directlywith radial passage 68 and thus with the described port 66. The fitting73 extends radially-inwardly sufficiently far to prevent flow of gas topassage 71.

The second fitting 74 is shown in FIGURES 3 and 6, having an axialpassage 7-7 and a plurality of radial ports 78, at least one of thelatter being in communication with passage 71 regardless of the rotatedpositon of fitting 74. Fitting 74 also has a solid or blind tip 79(FIGURE 6) which is inserted into passage 68 toprevent flow of gastherethrough to port 66. i

The fittings 73 and 74 are connected selectively to a conduit 80 leadingto a suitable source 81 (FIGURE 1) of gas under pressure. When the gassource 81 contains a monatomic gas, such as argon or helium, the fitting74 (FIGURES 3 and 6) is employed in order to cause the gas to beintroduced through passage 71 and port 67. Thus, a vortical or helicalflow is created having a large for-ward or axial component. When the gassource 81 contains nitrogen, hydrogen or other diatomic gas, fitting 73(FIGURE 7) is employed to effect flow of gas through passage 68 and port66. Thus, as described above, the inflow of gas is substantially radial,there being only a small axial component. When the source 81 contains amixture of diatomic and monatomic gases, the fitting selection isnormally determined by the gas which predominates in the mixture. Thus,if the mom atomic gas (such as argon) predominates, fitting 74 isemployed.

It has been found that the described selective use of different types oftangential-inlet ports (for dilferent gases) produces important results,including substantially increased electrode life.

Proceeding next to a description of the very important means forinjecting coating material into nozzle insert 47, for entrainment intothe plasma resulting from heat ing of the arc gas by are 65, thiscomprises a passage or port 82 (FIGURE 3) which is formed generallyradial ly through insert 47 and communicates with passage. portion 49 inspaced relationship from the downstream end thereof. The inlet intopassage 49 from radial port 82 is spaced substantially farther from thedownstream end of insert 47 than is the case relative to conventionalplasma-spray apparatus. Such increase in the distance through whichpowder passes within passage portion 49 permits adequate heating andaccelerating of the powder despite the fact that the gas flows at veryhigh velocities as will be stated hereinafter. The region of passageportion 49 downstream from port 82 should not be divergent, so that thehigh gas and powder velocities will be maintained in such region.

It has been found that the radial passage 82 should incline slightly, ina forward or downstream direction (FIG- URE 3), in order to achievedesirable entrainment of the powder into the plasma without creatingundesired backpressure, plugging or other effects. More specificially,the passage 82 may be at an angle of approximately degrees from thelongitudinal axis of passage portion 49 (10 degrees from a plane whichis perpendicular to the axis of passage portion 49). As indicated, theinner end of passage 82 is closer to the downstream end of the nozzlepassage than is the outer end of the passage 82. The axis of passage 82preferably intersects the longitudinal axis of passage portion .49 (bothlying in a vertical plane).

Passage 82 communicates with an additional passage 83 which is formedthrough the member 31, is being assured that these passages registerbecause of the above-indicated set screw 48 (FIGURE 4) and cooperatingconical recess in the insert 47. Passage 83, in turn, communicates witha powder-injection conduit 84 leading to a suitable powder source 86which is schematically shown in FIGURE 1. A source of carrier gas forthe powder from source 86 is indicated schematically at 87 in FIGURE 1,being connected to powder source 86 through a conduit 88. Thus,

powder from source 86 is entrained into gas passed therethrough from gassource 87, and the combination gas and powder are conducted throughconduit 84 and passages 83 and 82 to nozzle passage portion 49. Onedesired form of powder source 86 will be described subsequently withreference to FIGURES.

Referring next to FIGURE 3A, a second nozzle insert 47a is illustrated.Such insert may be identical to that shown in FIGURE 3, except that thediameter of the downstream passage portion 49a.is somewhat larger thanin the case of passage portion 49 of FIGURE 3. Insert 47a is employedwhen it is desired to spray ceramics, as distinguished frommetals, thereason being that the largerdiameter passage portion 49a decreases thegas pressure somewhat and thus permits the ceramic powder to bemaintained in portion 49a for an additional period of time required topermit effective and adequate heating thereof. Instead of employingdiiferent inserts 47 and 47a for metals and ceramics, it is within thescope of the invention to change other factors, including gas pressureand power level.

Mounted on the forward or downstream end of the torch, namely on thelarge-diameter cylindrical portion 34 of member 31, is a generallycup-shaped gas conductor 90 having a large-diameter cylindrical upsteamsection 91, a frustoconical intermediate section 92, and asmallerdiameter cylindrical downstream section 93. The inner diameter ofupstream section 91 corresponds generally to the outer diameter ofportion 34, so that the gas conductor may telescope over portion 34 asindicated. Thus, conductor 90 is locked in position by means of a setscrew 96, gas leakage being prevented by an O-ring 97.

The smaller-diameter or outlet portion 93 of the gas conductor 90defines a round outlet opening 98 (coaxial with passage portion 49) thediameter of which is much larger (for example, approximaly 2 timeslarger) than the diameter of nozzle passage portion 49. Furthermore,opening 98 is spaced away from the downstream (forward) end of insert 47by a considerable distance, such distance being shown as somewhatgreater than the spacing between powder inlet 82 and the downstream endof insert 47. The interior wall of gas conductor 90 at thesmaller-diameter outlet end 93 thereof is shown as being rounded, asviewed in section, in the general manner of a nozzle.

An additional gas source, indicated at 99 in FIGURE 1, communicatesthrough a conduit 100 with the gas conductor 90. More specifically,conduit 100 communicates with a port in the large-diameter cylindricalportion 91 at a slightly forwardly-inclined angle.

of conductor 90, such port being located radially outwardly from aprotuberant or axially-extending downstream end of insert 47. Asillustrated, such. downstream end extends a considerable distance awayfrom the front face of member 31. V

The gas conductor 90 performs important functions relative to aiding incollimating the plasma which discharges from passage portion 49,preventing undesired oxidation or other effects relative to the powderentrained in such discharging plasma, cooling the workpiece orsubstrate, and blowing away any loosely-adherent particles from theworkpiece or substrate so that the adherence of the coating to thesubstrate is improved.

It is'emphasized that the set screw 96 facilitates removal of the gasconductor 90, for example when it is desired to change nozzle inserts 47by loosening the set screw 48 (FIGURE 4). When the gas conductor 90 isin mounted condition, it conceals and prevents loosening of the outerend of the set screw 48.

Method of high-velocity spraying Stated generally, the method of theinvention comprises increasing the mass flow and enthalpy of anareheated gas to such values that a coating substance entrained thereinwill be accelerated to a velocity of at least 250 feet per second,introducing into the gas a coating substance adapted to be acceleratedthereby to at least such velocity, and impinging the entrained coatingsubstance against a workpiece or substrate. Stated more specifically,the coating substance is in the form of a fine powder having a particlesize on the order of 75 microns or less.

The method further comprises introducing the coating powder into thenozzle passage at a point a relatively long distance upstream from theoutlet end thereof, and Furthermore, the method comprehends employing anauxiliary gas-conductor downstream from the nozzle passage and passingauxiliary gas through such conductor for purposes including improvingthe collimation of thepowder particles in the discharging plasma,protection of the powder from oxidation and other effects, cooling ofthe workpiece, and removal of loosely-adherent particles from theworkpiece. Additionally, the method comprehends employing nozzles havingdifferent size passages in accordance with whether the entrained powderis metal or ceramic. The gas is passed through the nozzle passage in avertical or helical manner.

The enthalpy, powder-injection point, gas flow, and other factors shouldbe so regulated and correlated that the spray powder is melted but notvaporized. The melted particles, in impinging against the workpiece athigh velocity, form an extremely dense and smooth coating which adhereseffectively to the substrate. Using the present method, coatings havebeen formed which are smooth to within less than 10 microinches (lessthan 10 microinches difference after finishing between peaks and valleysof the coating surface).

The are gas is selected from a group consisting of argon, helium,nitrogen, hydrogen and mixtures thereof. A preferred are gas (introducedthrough vortex chamber 18) comprises a mixture of argon and hydrogen,with the argon predominating. The hydrogen produces the effect ofincreasing the enthalpy of the plasma and thereby accelerating the spraypowder particles to a much greater extent than would otherwise be thecase. The mixture is preferably about 90 percent argon, 10 percenthydrogen. However, the mixture may also comprise (for example) 65percent argon and 35 percent hydrogen, or 50 percent argon and 50percent hydrogen.

As indicated above, the spray powder is introduced in finely-dividedform, less than 75 microns particle diameter. The particle size may alsobe only a few microns, ,or even less than one micron. The decrease inparticle size permits melting of the particles in a very short period oftime, and increases the particle-acceleration effect because of the lowparticle mass.

The manner of feeding and injecting the spray powder is important to themethod. The powder-introduction port or passage 82 may be, for example,approximately /8 inch from the downstream end of passage portion 49(FIGURE 3) when the diameter of such portion 49 is on the order of0.21-0.28 inch. As previously indicated, the smaller diameter of nozzlebore 49 is employed for particles which are more readily melted, forexample metals, because the residence time of the particles in theplasma is decreased. For more refractory materials such as oxides, theinsert 47a (FIGURE 3A) having a larger bore 4% (such as 0.28 inch) isemployed because the larger bore decreases gas velocity somewhat andthus increases residence time and heating effect.

The amount of gas employed to entrain powder and carry the same to portor passage 82 should be maintained at a minimum. For this reason, it ispreferred that a screw-type powder source 86, not an aspirator-type, beemployed. Referring to FIGURE 8, a powder hopper 101 containing powder102 is provided with a feed screw 103 rotated by motor 184. Screw 103feeds the powder at a predetermined rate from hopper 101 to a chamber185 into which argon or other powder-carrier gas is supplied by theabove-indicated pipe or conduit 88. The powder-gas mixture then flowsthrough a venturi or restrictor 106 and a suitable mixing device 107(such as a cyclone mixer) to the above-indicated conduit 84 leading topassage 83 and thus port 82 (FIG? URE 3). With the described apparatus,and equivalent apparatus, a predetermined rate of powder feed may beachieved with relatively low requirement for argon or other carrier gas.i

As an example, the amount of carrier gas for the powder may be on theorder of about one cubic foot per minute at a pressure of about 5 psi.gauge.

To achieve high particle velocities, the mass flow is caused to be highas above stated. For example, the arc gas may be fed through chamber 19at a rate on the order of 2 c.f.m. at a pressure of 20 p.s.i.g. Muchhigher pressures and flow rates may be employed.

The current supplied by source 61 (FIGURE 3) should be high, for exampleon the order of 275450 amperes or higher, the voltage being on the orderof 60 volts. Thus, the power in the illustrated torch apparatus may bein the range of about 16 kw. to about 27 kw. or more.

The flow of gas through the auxiliary gas-conductor may be on the orderof 3545 s.c.f.h. (standard cubic feet per hour). In some cases, no gasis fed through conduit and the auxiliary conductor 98 except that whichemanates from the nozzle bore 49. Nevertheless, the auxiliary conductor90 performs important shielding and other effects. The gas passedthrough conduit 108 is normally inert, such as argon. However, in somecases such gas may be one adapted to create a desired chemical reaction,as distinguished from preventing oxidation.

The relationships are caused to be such that, as above indicated, theparticle velocity at a region three inches from the nozzle outlet is atleast 250 feet per second. The velocity may also be much higher, forexample 800 feet per second, or sonic.

Referring to FIGURE 1, the workpiece or substrate is indicated at W, andthe applied coating at C. The work may be located a few inches fromopening 98. It is a feature of the invention that the discharging plasmais characterized by a surprisingly small cone angle. Thus, spraying maybe efiected precisely, on any desired small or large area, without wasteor overspray. Access to various interior surfaces is also greatlyfacilitated.

It is to be understood that many of the advantages of the invention maybe achieved with particle sizes larger than those indicated. It is alsopossible to employ a majority of particles in the indicated range, mixedwith a certain percentage of particles of larger sizes.

It is within the scope of the invention to connect an additional (oralternative) power source between electrode 16 and/or 47 and thesubstrate W. Also, it is within 2. An electrical plasma torch, whichcomprises:

an elongated nozzle electrode insert having a passage therethrough,

a rear electrode,

nozzle means to mount said insert and said rear electrode in the scopeof the invention to provide one or more addicoaxial relationship, tionalpowder-injection ports 82, and inject therethrough said last-named meansincluding an insert-mountthe same or a different powder than that beingpassed ing element adapted to removably receive said through theillustrated port 82.. Thus, for example, alloyinsert, 1ng may beachieved in the plasma et. means to maintain a high-current electric arebetween As specific examples of the present method and apparasa1d rearelectrode and said insert, tus, reference is made to the following tablegiving repmeans to pass gas through sa1d nozzle passage in saidlggsentittive IdataI.I In all Ifases, the arc voltage is about insert,an; 1 f

vo ts. n a cases, t e arc gas is 90 percent argon, means to e ectcontinuous circu ation 0 water in op- 10 percent hydrogen, whereas thegas passed through con- 5 posite directions and radially-outwardly ofsaid induits 84 and 100 is argon. Gas may be introduced sert, throughthe auxiliary conductor 90 at a rate of about 35 said last-named meansbeing such that said water s.c.f.h. The table represents use of themethod withthe flows over at least a portion of the exterior ofillustrated apparatus, including the screw-type powdersaidinsert-mounting element and also flows feed means shown schematically inFIGURE 8. through a plurality of passages 111 said insert- Current AreGas Through Powder Deposition Deposition Powder (amperes) Chamber 18Carrier Gas R tFefl/hr Rate,1b./hr. Izlfiiciengg a e, percen TungstenCarbide (12% Cobalt)" 275 1.2 c.t.m. at 20 p.s.i.g 0.8 0.1. 8. 5 3.4 40.0 D0 300 1.2 e.f.m. at 20 p.s.i.g. 0.8 c.f. 12.0 6. 4 53. 3 Tungsten.-.450 1.2 e.f.m. at 20 p.s.i.g 0.8 c.f. 12.4 2.8 22. 6 Nichrome V 275 1.2c.f.n1. at 20 p.s.i.g 0.8 c.f. 5. 8 2. 6 44. 9 D0 250 1.2 c.f.m. at 20p.s.i.g 0.8 e.f. 6.8 3. 4 50.0 Zirconium Oxide 275 1.2 c.f.m. at 15p.s.1.g 0.3 e.f. 6.7 0.5 7. 5 Aluminum Oxide. 400 1.2 c.f.m. at 15p.s.i.g- 0.3 e.l. 4. 7 0.8 17.7 NichromeV 275 1.2 c.f.m. at 15 p.s.i.g0.3 c.f. 8.6 6.4 74. 5

The particle velocity measurements recited in the presmounting element,ent specification and claims were made in the ambient said passagesbeing disposed adjacent the exatmosphere, 3 inches from the forward oroutlet end of terior surface of said insert. the nozzle insert 47. Suchvelocities are much less than 3. An electric plasma torch, whichcomprises: those to which the particles are accelerated as they leave, anozzle electrode having a nozzle pass-age therethe nozzle passage. Thevelocity recitations in the apthrough, pended claims refer to suchvelocities 3 inches from the 40 a rear electrode, nozzle outlet. A meansto define a gas-vortex chamber communicating The foregoing detaileddescription is to be clearly un- Withsaid nozzle passage and coaxialtherewith, derstood as given by way of illustration and example sa1dgaSV0rt X am having a Wall Which is only, the spirit and scope of thisinvention being limited surface of revolution about the central axis ofsolely by the appended claims. said nozzle passage,

We claim: 7 first inlet means communicating generally tangentially 1. Amethod of operating a gas-vortex electrical plasma 'With said gas-vortexchamber and disposed in a plane torch on different types of gases and insuch manner that which is generally perpendicular to the common axisbenefits including maximum electrode life are achieved, of said chamberand said nozzle passage, which comprises: second inlet meanscommunicating generally tangenproviding an electrical plasma-jet torchhaving a gastjally ith id gaswortex h b Vortex chamber commumcetmgaxlany Wlth a nozzle said second inlet means being inclined forwardly Pa relative to said common axis whereby gas introsaid torch alsohaving anelongated rear electrode duced through Said Second inlet means flows t ii i of siald ig a b helically in said gas-vortex chamber and with mamammg. an 6 cc me are m Sal mom 6 passage ea relatively long lead betweenturns of the helix, tween said rear electrode and another electrode, andmeans selectively adapted at different t1me periods introducing, dur1ngperiods when 1t is desired to opert t duce tian diam i 0a th u h ate thetorch with a gas which is essentially diatomic, h 5 t an 3 y i s anessentially diatomic gas into said gas-vortex rs m e {means an essen lay monlormc e through said second inlet means, and means to malnchamberand generally tangentially thereof,

said gas flowing vortically and helically in said gasvortex chamber anddischarging through said nozzle passage, and

tain a high-current electric are between said rear electrode and anotherelectrode. 4. The invention as claimed in claim 3, in which said meansto introduce gas selectively through said first and second inlet meanscomprises a plurality of gas-inlet fitsaid rear housing element having acentral stem portion inserted through said body into said vortexchamber,

an elongated rear electrode insert disposed in an axial passage in saidcentral stem portion,

a removable plug threadedly inserted into said rear housing element andadapted to lock said rear electrode insert in position,

a front housing element having a rim portion mounted to said insulatingbody,

an electrode-mounting and coolant-conducting element mounted to saidfront housing element,

said last-named element having formed therethrough a nozzleinsert-receiving bore,

said last-named element also having formed therethrough a plurality oflongitudinally-extending circumferentially-spaced coolant passagesdisposed adjacent said bore,

coolant separator means extending between said electrode-mounting andcoolant-conducting element and the interior wall of said front housingelement,

said coolant-separator means dividing said front housing element intofront and rear coolant chambers,

means to introduce coolant into said front coolant chamber forcirculation forwardly and exteriorly along said electrode-mounting andcoolant-conducting element and subsequent circulation in a rearwarddirection through said circumferentially-spaced passages to said rearcoolant chamber,

means to conduct coolant from said rear coolant chamber through saidinsulating body to a coolant chamber defined by said rear housingelement rearwardly of said insulating body,

means to drain coolant from said last-named chamber,

a nozzle electrode insert removably secured in said bore in saidelectrode-mounting and coolant conducting element,

means to pass gas through said vortex chamber for outflow through saidnozzle electrode insert, and

means to maintain a high-current electric are between said rearelectrode insert and said nozzle electrode insert.

6. A method of forminga dense, smooth coating on a substrate, whichcomprises:

providing an electrical plasma-jet spray torch having an elongated,generally cylindrical nozzle passage,

effecting flow of gas in said torch and through said nozzle passage tothe ambient atmosphere,

maintaining a high-current electric arc in said torch at such locationtherein that at least the downstream footpoint of said are is located insaid nozzle passage and is spaced a substantial distance from thedownstream end of said nozzle passage,

injecting a finely-divided particulate coating material into said nozzlepassage laterally through a wall portion thereof and at a locationbetween said downstream footpoint and said downstream end,

regulating said gas flow and the power in said are in such manner thatthe velocity of said particles, when measured at a location in theambient atmosphere three inches from said downstream end, is at least250 feet per second, and

directing said particles against a substrate to form a dense and smoothcoating thereon.

7. The invention as claimed in claim 6, in which said method furthercomprises effecting vortical flow of said gas in said nozzle passageabout the axis thereof.

8. The invention as claimed in claim 6, in which said gas flow and thepower in said are are also regulated in such manner that said particlesof coating material are softened but not vaporized.

9. The invention as claimed in claim 6, in which the majority of saidparticles of coating material have diameters no greater than 75 microns.

10. The invention as claimed in claim 6, in which said gas comprises amixture of argon and hydrogen.

11. The invention as claimed in claim 6, in which said method furthercomprises effecting said injection of coating material at a locationspaced upstream from said downstream end of said nozzle passage.

12. Apparatus for effecting high-velocity spray deposition of a dense,smooth coating onto a substrate, which comprises:

first wall means to define a gas-vortex chamber,

the interior surface of said first wall means being a surface ofrevolution about a predetermined axis,

means to introduce gas into said chamber generally tangentially thereofwhereby to effect vortical flow of said gas in said chamber about saidaxis,

second wall means to define an elongated nozzle passage communicatingwith said chamber,

the interior surface of said second wall means also being a surface ofrevolution about said axis, the portion of said nozzle passage adjacentsaid chamber being generally frustoconical and converging in a directionaway from said chamber, the portion of said nozzle passage remote fromsaid chamber being generally cylindrical,

said cylindrical passage portion extending from the small-diameter endof said frustoconical passage portion to the ambient atmosphere, anelongated rear electrode extending axially of said chamber into saidfrustoconical passage portion,

the forward end of said rear electrode being spaced radially-inwardlyfrom said interior surface of said second wall means, means to maintaina high-current electric are between said forward end of said rearelectrode and an arcing region of said interior surface of said secondwall means,

said arcing region being spaced a substantial distance upstream from thedownstream end of said cylindrical passage portion,

a powder-injection port provided in said second wall means between saidarcing region and said downstream end of said cylindrical passageportion, and

means to inject through said port into said cylindrical passage portiona finely divided spray powder adapted to be applied to a substrate,

said gas-introduction means and said arc-maintaining means effectingsoftening but not vaporizing of said injected spray powder, and furthereffecting acceleration of said powder to such velocity that said powderwhen passed through the ambient atmosphere at a distance three inchesfrom said downstream end of said cylindrical passage portion istraveling at a velocity of at least 250 feet per second.

13. The invention as claimed in claim 12, in which said forward end ofsaid rear electrode is also generally frustoconical and coaxial withsaid axis, the surface of said forward end converging in a directionaway from said chamber.

14. The invention as claimed in claim 12, in which said powder-injectionport is spaced a substantial distance upstream from said downstream endof said cylindrical passage portion.

15. The invention as claimed in claim 12, in which said means to injectspray powder through said port includes a passage communicating directlywith said port and extending generally radially of said axis, said powerpassage being somewhat inclined relative to a plane which isperpendicular to said axis and extends through said port, .the directionof incline being such that the portion of said powder passage adjacentsaid port is more remote from said chamber than is the portion of saidpowder passage remote from said port.

16. The invention as claimed in claim 12, in which an auxiliary gasconductor is provided around said second wall means and has an annularmouth portion coaxial with said axis, said mouth portion being spaceddownstream from said downstream end of said cylindrical passage portion,the diameter of said mouth portion being much larger than that of saidcylindrical passage portion, and in which means are provided tointroduce gas into said auxiliary gas conductor independently of saidgasvortex chamber.

17. The invention as claimed in claim 12, in which water-cooled Wallmeans are provided around said second wall means, and in which saidsecond wall means is a 14 metal insert removably secured in saidwater-cooled wall means.

18. The invention as claimed in claim 17, in which first and second onesof said metal inserts are provided, said second metal insert having acylindrical passage portion the diameter of which is substantiallygreater than that of the cylindrical passage portion of said firstinsert.

No references cited.

ANTHONY BARTIS, Primary Examiner. RICHARD M. WOOD, Examiner.

1. A METHOD OF OPERATING A GAS-VORTEX ELECTRICAL PLASMA TORCH ONDIFFERENT TYPES OF GASES AND IN SUCH MANNER THAT BENEFITS INCLUDINGMAXIMUM ELECTRODE LIFE ARE ACHIEVED, WHICH COMPRISES: PROVIDING ANELECTRICAL PLASMA-JET TORCH HAVING A GASVORTEX CHAMBER COMMUNICATINGAXIALLY WITH A NOZZLE PASSAGE, SAID TORCH ALSO HAVING AN ELONGATED REARELECTRODE EXTENDING AXIALLY OF SAID NOZZLE PASSAGE, MAINTAINING ANELECTRIC ARC IN SAID NOZZLE PASSAGE BETWEEN SAID REAR ELECTRODE ANDANOTHER ELECTRODE, INTRODUCING, DURING PERIODS WHEN IT IS DESIRED TOOPERATE THE TORCH WITH A GAS WHICH IS ESSENTIALLY DIATOMIC, ANESSENTIALLY DIATOMIC GAS INTO SAID GAS-VORTEX CHAMBER AND GENERALLYTANGENTIALLY THEREOF, SAID GAS FLOWING VORTICALLY AND HELICALLY IN SAIDGASVORTEX CHAMBER AND DISCHARGING THROUGH SAID NOZZLE PASSAGE, ANDINTRODUCING, DURING PERIODS WHEN IT IS DESIRED TO OPERATE THE TORCH WITHA GAS WHICH IS ESSENTIALLY MONATOMIC, AN ESSENTIALLY MONATOMIC GAS INTOSAID GASVORTEX CHAMBER AND GENERALLY TANGENTIALLY THEREOF, THE DIRECTIONOF INTRODUCTION OF SAID MONATOMIC GAS BEING FORWARDLY INCLINED INCOMPARISON TO THE DIRECTION OF INTRODUCTION OF SAID DIATOMIC GAS WHEREBYTHE GAS HELIX RELATIVE TO SAID MONATOMIC GAS HAS A SUBSTANTIALLY GREATERLEAD OR PITCH THAN IN THE CASE OF THE HELIX RELATIVE TO SAID DIATOMICGAS.